Telemetering transmitter for a projectile



March 10, 1959 A, v AST|N 2,877,452 I TELEMETERING TRANSMITTER FOR A P ROJECTILE Filed Oct. 7, 1944 3 Sheets-Sheet 1 FIG.

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INVENTOR l i i ALLE/v u Asn/v l l ATTORNEY March 1o, 1959 A. v. ASTIN 2,877,452 TELEMETERING TRANSMITTER FOR A PROJECTILE Filed 001'.. 7, 1944 3 Sheets-Sheet 2 FIG. 2

INVENTOR ALLE/V Y AST/N BY I l() ATTORNEY March 1o, 1959 A, v ASTIN 2,877,452

'IELEMETERING TRANSMITTER FOR A PROJECTILE Filed Oct. 7. 1944 FIG. 5

INVENTOR ALLE/V V; AST/N 'ATTORNEY 3 Sheets-Sheet 3 'l TELEMETERING TRANSMITTER FOR -A PROJECTHJE Allen V. Astin, Bethesda, Md., assigner to. the United States of America as'represenatedv by the Secretary of th'eNavy Application October 7, 1944, Serial No. 557,712 2 Claims. (Cl. 340-.-208) (Granted underTitle 35, U. S. Code (1952), sec. 266) This invention relates to a radio sonde for an airborne vehicle, and particularly to telemetering transmitters adaptedto furnish Lat a remote pointa continuous record, bothqualitativeandquantitative, of conditions prevailing at "the point vof,V transmission.

'Anobject of the `invention is lto provide ar radiotransmitter so'compact and rugged in' its naturethat it may be incorporatedin a bomb' lor'projectile 'and which functions whilethebombor'projectile is in flight. It will readily be appreciated, however, that the apparatus of th'e inventions-equally applicable to the-automatic transmission of desired infomation under conditions less rigorous.

The embodiments of the invention herein disclosed areso arranged? and constructed asto be adapted for installation in explosivey ordnance` equipped with prox imitytiring' or fuzing means, and-to function in such manner'ats-continuouslyV to transmit an indication 'of the 'unctio'ning of," andthe conditions prevailing in, such proximity ring' or fuzing apparatus; TheY record thus automatically'transmitted:` may bey recorded on paper, iilm orfinanyoth'er convenient manner to permit con"- venient study.`

An' important object-of the invention -is to provide' an automatic radio transmitting andoscillation generating mechanism of extremely compact and rugged construction; the partsfofwhich are so designed that steady; uniform and accurate comparative record transmission is provided/throughout the YHight of abomb or projectile carrying the same.

Another objectv of the invention isA to provide radio signal generating meansx so constructed that itrx automatically incorporates with the transmitted signal al comparison pulseL orsignalfofi knownamplitude, by means of' which the magnitudev of significanty currents 'existing in-fuzing.' circuits orother apparatus to be checked-may be.` gauged Another object is vto-progvide a radio signal generator which-vis adapted 'to furnish :a eontinuousindicationof theopcration-.of a ph'otooell, or-of electrical components ofrphetoclectrie proximity fuzes lduringiiight 'of a projectile containingtthe same;r whereby'there may-bev obtained at alremotestation a continuous record of' the photocellacurrents prevailing' throughout a =desired time, as during the operation( ofthe photo-electric-` fuzing means? Anotherf object ofithe presentiinvention is -to provide improved 1 means whereby` a 1 battery or electrolytic cell maya-bet accurately testedlfr'omc a` remoteipoint.

Another-.'objectisfto providef an improvedfdevice`V of thev character indicatedfzwhich 'eliminates theinterfering etiectsbf.V radiation- -reliecte'd' yby'v objectsv passing; ori 'near the source of radiation An object xrelated: .totthat last stated: is to provide t apparatus.- ofc the..k indicated character.A employing l' frequency rnodulatitm,` the.` arrangement4 being such.` that sources ofl ,reflectivefand,` other` interference.` aregpreventedafrom hamperi-ng-the effective voperation of,v the. apparatus.

tlfr objects and`advantages Wilfbecomeapparent es Patent' 2"' uponconsideration-of the presentdi'sclosure in its entirety.

In the drawings:

Fig. 1 isa. schematic diagram of a radiotransmitting system employing, amplitude modulation and constructed in accordance .with the present invention; ,v l

Fig. 2 is a schematic diagram of a-moditied arrangement in which `frequency modulation -is employed, with means for adjusting. the frequency by varying the grid biasing effect ofthe input signal;

Fig. 3is a similar'schematicdiagram of another modied'construction employing crystal control ofthe carrier frequency;

Fig. 4 is aI schematic diagram of another modified arrangement adapted'toreport conditions prevailingin a circuit incorporating a photo-electric' cell;

Fig. 5 is a 'partly' diagrammatic lview'correspondingf'to a longitudinal 'diametrie'section' of the"no`se`portion of an aerialbombJ providedwithian inductance tuned antenn'al adapted yto'serve a'sthe radiating system for -a radio transmitter vconstructed inaccordance withthe present invention;

Fig. 6 is a simil'afview' showing a' capacity tuned antenna mounted uponthe nose of a bomb;

Fig. 7 is .a similar view of the nose portion ofarocket projectile'l provided with antenna'means streamlined to coincide with the nosefof the projectile;

Fig. 8 is a fragmentary perspectiveview' of the ta'il portion of a bomb equipped with radio transmitting means constructed"ini-accordance`with the' present'inl vention, and provided "with an'antenn'a of "another'somewhat modified 'coristructiorn Figs: 9," 10, llz andy l2" areoscillograms o ii records' transmitted' by theA improvedl lradio transmittingl mechanisms under varying conditions; and

Fig. 13 illustratesuse of-the embodiment of Fig. 2 for transmittingfchanges in potential.

The amplitude modulated circuit of" Fig. l consists essentiallyof a standard signal generator, modulator 'and carrier *oscillator portions, generallydesignatedy S,y M and C, respectively. TheV output of" the carrier oscillator feeds a dipole'antenna' system, consisting-offthefantenna properand the bomb or rocket casing, tlieantenna system beingwcoupledi'toitheoutput off the 'carrier voscillator by mean'sf of inductance 2'2and-p1a`1te'coil21.-` The carrier frequencyis adjustable by"means of-a'-va'riable'condenser 23which provides-coupling betweenandis corrnected-to the plate-coil 21 andgrid coil 2`4fof the carrier oscillator tube 25,' the'fcondenser beingv connected* to each coil near the midpoint thereof.

The output? of theradio proximity fuze,or other device to'be tested, is fed -to the modulator Mat point '26; and signals generatedfby'the radio fu'ze systemare thereby impressed upon` the: carrier output and `radiated there# with'by the dipole, in'the mannerclearlyindicated'in thedia'gram Fig. l.

A standard orcomparison signal is also radiated with thecarrier, beingvgeneratedby 'the signal generator' S, which4 is i arrangedtol operate as a blocking oscllt'o'r Theroutput `of the blocking oscillator S is 'fedi to the'fgrid offmodulator`27` in parallel with the output signal from the fuze; The amplitnde'of'the pulse 'of the blocking oscillator can thnslbeusedlas a standardof-comparison at the receiving-station, permitting the output olf'tlieifl'lfev to -be compared with it` to furnish anindication of the ampltude-othe fuze output.

The .periodic blocking action= results vfrom the arrangement -oresistance 44 and capacitance'AS fin' paralleliin the gridcircuit otube., 46.y Thev grid and lplate-:coils 47,. 48.*of signa-l generator tube 46are inductively=coupled, `as indicatedjin dotted-lines. When the-tube .46 is inrfthe oscillating condition, its grid swings positive in each half cycle,` and during each such electrons from the grid circuit, ment 49, resistance 44 and condenser 45. The rate of accumulation of electrons, which tend to bias the grid negatively, depends upon theamplitude' of oscillation and the value of condenser 45. The value of resistance 44` does not appreciably Aaffect this rate since, in the oscillating condition, the grid-iilament resistance is relatively low. As the grid accumulates electrons it becomes progressively more negative with respect to filament 49 until the negative bias is suflicient to block the tube from oscillating. At this instant an excess of electrons is accumulated on the grid and connected plate of condenser 45. When oscillation has ceased there is no longer a positive driving potential in grid coil 47, so that the accumulated electrons on the grid and connected condenser plate leak oi to ground through resistance 44. When sutlicient electrons have left the grid to raise its potential to within the oscillating range, the tube will again break into oscillation and the cycle will be repeated.

It will be apparent that the pulsing period of thesignal generator can be adjusted by changing the value of resistance 44 or condenser 45, since the former affects the rate of leakage of electrons to ground, and the latter determines in part the rate of accumulation of electrons by the grid, the grid-lament potential difference being established largely through condenser 45, for high frequencies.

While suitable values for the various circuit components of Fig. l have been shown, it will be understood that these may be varied as conditions may dictate. The values of the plate and grid circuit components of the transmitter tube are adjusted to give maximum ratio of amplitude to frequencyy modulation and also to provide as wide as possible a range of linear modulation, since the presence of frequency modulation in an audio modulation system is undesirable when quantitative measurements are desired.

The presence of appreciable frequency modulation evidences itself by a tendency of the phase of the audio output of the receiver to reverse at some point in the tuning range. At the point of reversal, the effective modulation will be zero oriapproximately zero, minimum audio output is frequently near the maximum carrier indication so that it is then impossible to use the carrier indicator on the receiver as a tuning indicator, and tuning must be done by adjusting for maximum ampli- ,tude of the standard signal as viewed in theoscilloscope.

half cycle it accumulates The frequency of the standard signal generator pulse `may be approximately -five cycles per second. It will .be apparent that the amplitude is calibrated in ter-ms of a signal applied at the input 26 of modulator tube 27, the other input terminal being of course ground 28. The standard signal may conveniently be made equivalent lto about five volts, applied to the grid of tube 27, and the modulation is linear in response up to eight or ten volts applied to the grid of this tube. If it is desired to measure higher voltages, a potential divider can be introduced in the grid circuit to extend the range, although this would also increase the effective noise level.

Fig. 9 shows a laboratory test calibration of the apparatus of Fig. l as given by an oscillogram made during an actual test of the apparatus. The sharp regular pulses 29 are those resulting from the action of the signal generator S for comparative purposes, while the single larger pulse 30 represents an actual positive five volt pulse signal applied at input 26 of the modulator tube 27.

An oscillographic'record of an actual drop test on a radio transmitting apparatus of this type mounted in and dropped with a bombis shown in Fig. l0. In this case the comparison signals 31 Aare of the order of ve volts positive applied to the grid of the modulator, while the background pulses 32 are due to microphonics present in the radio transmitter system. The background pulses which includes the laand this i in this case amount to less than plus or minus three quarters of a volt. The record was made from` the last portion of an eight thousand foot drop, in which case the microphonics are most severe. For this unit the inodulation was linear up to eight volts, giving an eight to one range for dependable voltage measurement. The regularly spaced dots 33 were made by a neon light actuated by a 60-cycle currentsource to serve as a time scale on the oscillogram.

While the mechanical mounting and disposition of the circuit components is a matter of choice, the unit is preferably dipped in paraffin or other wax to prevent vibration of the circuit parts, although it may be sufcient to bind only the radio frequency components with the wax.

Certain limitations are involved in the use of high frequency amplitude modulation in radio transmitting apparatus of this class, due to interference between direct radiation from the apparatus and reected radiation. When the mechanism is contained in a bomb, reection from the bomber occurs, and persists to approximately 1000 feet below the bomber; even at this distance amounting to approximately 2 percentyofihe modulation. Retlection also occurs from the target or any other object which the apparatus may pass. The amplitude of the interference peaks decreases and their frequency increases with time, the peaks being one half wave length apart in the path of the falling'bomb. The presence of `this interference handicaps the use of any tests other than those in which the bomb or projectile is free in flight. o

Considerable interference is encountered in the operation of apparatus constructed as above described, and it may for the indicated reasons be desirable to employ frequency modulation, which may be done by adjusting the constants of the transmitter components to give maximum frequency modulation. When `frequency modulation is used interference signals due to reections from the bomber and other objectsI are eliminated, the interference being primarily amplitude modulated. VA frequency modulated radio transmitter may therefore be used for tests against targets. A further advantageis that tuning can be made on the carrier indicator. Although trouble from microphonics is somewhat more pronounced in the case of frequency modulation, this can be considerably reduced by `shock-mounting the device.

Fig. 2 shows a frequency modulated arrangement in which the frequency of the audio oscillator A used as a standard or comparison signal generator can be varied by changing its grid bias or grid resistance. The fuze signals or other signals to be measured are applied directly to the grid of tube` 34 at point 35 and at ground 36A. Tube 34 modulates the carrier developed by the oscillator tube 36. An audio signal is obtained Whose frequency is a function of the grid bias.

Grid andplate coils 37, 338 of the carrier oscillator are inductively coupled, as indicated. A tuning condenser 39 is used, as in the embodiment previously described. The grid and plate coils 40, 41 of the signal Igenerator A are also inductively coupled, and the dipole 42 is inductively coupled to the plate coil 38 of the carrier oscillator by means of coil 43.

Resistance 50 is connected in the grid circuit of tube 34 in parallel with condenser 51 so that the audio or modulating frequency of tube A can be adjusted by changing the value of resistance 50 or capacitance 51. The signals applied to the grid circuit at point 35 will therefore alter the grid bias 'to change -the frequency of oscillation of circuit A and this change will be transferred to the carrier developed in circuit C.`

The embodiment of Fig. 2 may also be used as illustrated by Fig. 13 to transmit changes in the potential of a battery. For this purpose a resistance 61 is connected between the points designated PQ of Fig. 2, the battery 60 being connected across the resistance as` shown in this type of apparatus fory asa'maa Fig. 13.- Ghanges inr thfe'f*batteryfpotentialwill therefore be retlected-fas-analtered grid bias .of tube 34a.

Fig. 11 isr an oscillogram ofthe signal from. afrequen'cymodulated' radio transmitterv oflthe type shown in Figff2, the Ytransmitter mechanism being connected to a' radioiproximity fuze in a born-b, shocklmountedin the bomb andl dropped therewith froman altitude of* 8000 feet; The'amplitude ofthe comparison signal Was approxjimately 3.5 volts, andthe noise level was below plus forgminus one volt.

Itlh'asalso been found that much ofthe interference due, .to1refl`ection'from the target, as well as from the bomber', .canbe avoidedby using lowerv carrier `frequencies'withi amplitude'modulation. The reduced frequency permits the use of:la.crystal controlled oscillator, affordingr. excellent :amplitude modulation, and when frequencies of the order of two to three megacycles per second are used no target interference is observed. A circuit diagram of a transmitter of this type is shown in Fig, 3. In this embodiment the oscillator tank coil 5'6 also serves as a loop antenna. The loop may be wound about the tins of the bomb, as shown in perspective in Fig. 8. Crystal 57 is connected in the grid circuit of the carrier oscillator to control the carrier frequency, as shown.

The modification of Fig. 4 may be used to transmit to a remote point measurements of the current being passed by a photo-electric cell. In this manner it is possible to check the action of a photo-electric proximity fuze while in flight. The photo-cell 54 (which may be the photocell which also forms -a part of a fuze mechanism) is connected to the audio oscillator circuit in the manner shown. The anode of the photo-cell is connected to the positive B battery supply, and the cathode to a terminal of grid coil 52 leading to the grid of tube 53. The carrier oscillator C will be seen to be arranged as in the previous embodiments. The varying current through the photo-cell 54, under different light conditions, changes the grid bias of tube 53 since electrons are supplied to the cathode of the photo-cell by passing from the filament to the grid of tube 53 and thence through the grid coil 52 to the photo-cell. The rate of leakage of the electrons from the tube grid, which determines the bias and consequently the frequency of oscillation, will depend directly upon the rate of flow of electrons from the cathode to the anode of the photo-cell, which rate is proportional to the light flux received by the photo-cell cathode. The frequency range for a given range of photo-cell currents can be varied by adjustment of the capacitance 55 connected between the photo-cell terminal of grid coil 52 and the ground, since this capacitance is connected in sexies with coil 52 in the grid circuit of tube 53.

Fig. 12 shows at 70 the target pulse in a test of a photo-electric fuze dropped against Ia drone target, as recorded upon an oscillograph controlled by a circuit of the type illustrated in Fig. 4. The mechanism was shock mounted and frequency modulation was employed, with a nose antenna.

Figs. 5, 6 and 7 show alternative `antenna constructions usable in conjunction with apparatus constructed in accordance with the present invention. In Fig. 5 the antenna tip 1, of brass or the like, is mounted in a plastic insulating rod 2 which is suitably attached to the nose of the bomb 3 from which the antenna assembly projects in coaxial position. The inductive antenna portion 4 is wound upon rod 2 and connected to the brass tip 1. Antenna coil portion 4 is connected in series with the antenna coil 5, which is inductively coupled to the tank coil 6 of the carrier oscillator. The other end of antenna coil 5 and the inner end of antenna portion 4 are grounded to the bomb casing, so that the casing and antenna function as a radiating dipole. The length of the -wire in the tuning inductance 4 is approximately one quarter of the wave length of the transmitter, the antenna being of the inductance tuned type.

of the capacitance tuned; pported" in: aninsulati'ngl bushingv 8 andi4 in serieswith'fan antennaI 9'with'n1th'eV bomb body,l the antennaifcoilbeing connected in series withfthe rodi7' and 'with the bombbody and shunted by the tuning condenser 111 It/will b`e understood-that thek antennalcoilis:y energizedbyfthe tankfcoil, inductively coupled thereto and lfedf-fromy agcircuit-, ofonev of the forms previouslylde'scribed. f

Fig'. 7 v illustrates -an inductance `tuned rocket f antennal of a symmetrical formzwhichinvolvesstheiuse `oflnoprotuberances; which might-` interfereI with the4 ilightzchar acteristics.` of;` the rocket. The nose. cap portion` 12 of copperorftheflike'formsone section of they-antenna dipole and isv welded/or otherwisefastenedat itsbase to acopper disc. 13. which is.-` inv4 turn attached to.- the insulating sleeve or ogival section 14, screwed to and forming a smooth section of the remainder of the projectile. Axially disposed within the section surrounded by the insulating ogival portion 14 is a plastic or other insulating cylinder 15, shown as held in place by a screw 16 which transfixes the copper disc. Antenna coil 17 is wound upon the form 15, one end of the coil being attached to cap 12 and the other to the bomb casing 19. Also connected to the coil 17 is the antenna coil 18, which is coupled to the tank coil of the oscillator.

Where the impulses are slow enough to permit satisfactory visual observation, a frequency meter can be used, rather than an oscillograph, to receive the signals from the transmitter.

Frequency modulated transmitters of the class herein described are also useful in making preliminary surveys of acoustic type fuzes for bombs. In this case the output of a microphone is rectified by a diode and the volt age produced is applied to the input of the transmitter. The records of the received signals then show the sound level as a function of frequency.

It will also be understood that suitable filters can be used with these telemetering transmitters to suppress any undesired frequencies, such as microphonic disturbances, and that other variations are possible without departing from the spirit and scope of the claims hereto appended.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. In combination with an explosive missile, a signalling device contained within said missile for transmitting to a remote location signals controlled by the functioning of components of the missile during flight and comprising carrier wave generating means including an electron tube arranged in an oscillating circuit, pulse generating means coupled to said wave generating means for imposing upon the carrier wave an intermittent reference signal of known amplitude, separate means coupled with said electron tube for modulating the carrier wave by signals controlled by the functioning of components of the missile `during flight, said pulse generating means comprising another electron tube having cathode, grid and plate portions, feedback inductance means connected to the grid and plate portions of said last named tube and tending to cause oscillation thereof, and means comprising a frequency determining network connected to the grid portion to at least a part of said inductance means for periodically blocking said oscillation, said network being connected to said cathode portion.

2. In combination with an ordnance fuze, a telemetering transmitter comprising circuit means for developing a carrier wave; circuit means for generating an intermittent reference signal of a predetermined amplitude and including, a vacuum tube having at least cathode, plate and control grid electrodes, a D. C. supply for the cathode-plate circuit of said tube, a feedback circuit including a capacitance and resistance connected between the control grid and plate, electrodes of said tube for inducing oscillation of said tube, and biasing means for varying the bias voltage applied to said tube thereby to modulate the oscillatory frequency of said tube, said biasing means including a frequency changing network coupled to said control grid, a resistance coupled to said network and in the circuit with said control grid and cathode electrodes, and a voltaic cell shunted across said last recited resistance whereby voltage changes in said cell correlatively vary said bias voltage;` circuit means for effecting modulation of said carrier wave by said reference signal and a signal controlled by the operation of the fuze; and antenna means for transmitting the modulated carrier wave to a remote monitoring station.

8 References Cited in the le of this patent UNITED STATES v PATENTS Sweden Feb. 24, 

